1. Field of the Invention
The present invention relates to a novel toner containing a dimer of a diarylguanidine type compound for developing an electrostatic image in image formation in electronic photography, electrostatic recording, electrostatic printing, and the like.
The present invention relates also to a novel diarylguanidine type compound.
Various methods of electronic photography have been disclosed in U.S. Pat. No. 2,297,691, and Japanese Patent Publication No. 42-23910 (corresponding to U.S. Pat. No. 3,666,363), and Japanese Patent Publication No. 43-24748.
Image developing methods for electronic photography are classified roughly into dry developing methods and wet developing methods. The former is subdivided into methods employing a two-component developing agent and methods employing a one-component developing agent.
As toners for dry developing methods, used, fine powdery materials have been used comprising a dye and/or a pigment dispersed in a natural or synthetic resin. For example, as a one-component developing agent, a powdery toner of finely pulverized binder resin, such as polystyrene, in a size of approximately from 1 to 30 .mu.m in which a coloring agent is dispersed are used. For the magnetic toners, powdery magnetic materials such as magnetite are used. In the case of two-component developing agents, the toner is usually used in combination with a particulate carrier such as glass beads, powdery iron, powdery ferrite or the like.
The toner needs to be charged positively or negatively corresponding to the polarity of the electrostastic latent image to be developed.
For the purpose of giving an electric charge to a toner, triboelectric chargeability of the resin component of the toner may be utilized. In this method, however, the developed image is liable to be fogged because of low chargeability of the toner, giving unsharpened images. In order to impart the desired triboelectric chargeability to the toner, a substance for donating electric chargeability, called a charge-controlling agent, is added thereto.
Charge-controlling agents known in the art include compounds such as nigrosine dyes, azine type dyes, copper phthalocyanine pigments, quaternary ammonium salts, and polymers having a quaternary ammonium salt in a side chain for positive triboelectric charging.
Since some of these charge-controlling agents are liable to contaminate sleeves and carriers, the toner employing such an agent causes deterioration of its triboelectric chargeability and decrease of the image density with repetitive copying. Some kinds of the charge-controlling agents have insufficient triboelectric chargeability and are liable to be affected by temperature and/or humidity, causing fluctuation of the image density depending on change in the surrounding conditions. Some kinds of charge-controlling agents are poorly dispersible in the resin, so that the toner employing such an agent is liable to cause non-uniformity of triboelectric charge quantity between the toner particles, causing fogging. Some kinds of charge-controlling agents are poor in storage stability and may sometimes deteriorate the triboelectric chargeability during a long term storage. Further, some kinds of charge-controlling agents have color, so that they can hardly be used for color toners.
U.S. Pat. No. 4,663,263 describes a toner containing a guanidine derivative. The guanidine derivatives specifically mentioned in this U.S. patent are monomers, which are good positive charge-controlling agents but still have a room for improvement. Some known guanidine derivatives, for example, are found to contaminate toner supporters (e.g., a carrier and a sleeve) when the toner is pulverized to a size of about 3/4 or smaller of usual toner size (e.g., 13 .mu.m), causing gradual lowering of image density. Furthermore, conventional guanidine derivatives can hardly be used with binder resins of high acid value depending on conditions because of the reactivity of the derivatives with acids.